The invention relates to a method for measuring wear in the lining of a metallurgical vessel, for example, a ladle or a basic oxygen furnace.
It is extremely important to measure wear in the lining of ladles or basic oxygen furnaces or other industrial containers which are used for example in the steel making process. This renders it possible to optimize the service life of the container and to prevent excessive wear in the lining from causing risks pertaining to production or industrial safety. As an example, wear linings of basic oxygen furnaces must be renewed relatively often, as their life time varies, depending on what is melted in the basic oxygen furnace, on the material of which the lining is made, and naturally on the number of melts for which the basic oxygen furnace is used.
The wear in a lining is measured by a method based on measuring the time of flight or the phase shift of a laser beam. The laser beam is directed to the lining on the inner surface of the basic oxygen furnace, from which it is reflected back to the measuring device. In the method based on measuring the time of flight, the distance between the measuring device and each measured point on the lining to be measured in the coordinate system of the measuring device can be calculated on the basis of the time difference between the emitting time and the return time of the laser beam. The measured points define the wear profile of the lining, which may be output for instance to a display terminal, by which the wear profile measured from a basic oxygen furnace in process can be compared graphically and numerically with the profile that was measured on the safety lining of the container or the working lining before the container was actually brought into use, i.e. before the first melt.
To measure wear in the lining of three-dimensional objects, such as basic oxygen furnaces, ladles and other containers used in industrial applications, by non-contacting methods, such as laser measurement, requires that the measuring device and the object to be measured are represented in the same coordinate system. Combining the coordinate systems of the measuring device and the object to be measured is called fixing. In other words, the measuring device is positioned or fixed in relation to the object. For fixing it is necessary to use three or more permanent marks, with the laser beam of the measuring device being directed sequentially towards each permanent mark, and the coordinates of each permanent mark are measured in the coordinate system of the measuring device. Even if the measuring device has a fixed position in the vicinity of the container through permanent marks, it is advisable to perform fixing for each lining measurement again, which ensures a change in the ambient conditions and other factors not to cause any errors.
In the so-called direct method normally used for positioning or fixing, stationary fixing points, also called permanent marks, are part of the object to be measured, or can be mounted to the object, or in the vicinity of the object. By means of the permanent marks the coordinate systems of the object and the measuring device can be mathematically combined. In the direct method, the object to be measured and the measuring device can be included into the same coordinate system by measuring at the same time both the permanent marks and the points to be actually measured.
In a special case where the object to be measured is supported by a tilt axis, indirect angle measurement fixing can be applied, with the permanent marks being located on the container or outside of the container. An angle measuring device can be mounted, for example, to the tilt axis of the container or can be mounted elsewhere to the container. An example of such measuring device is a so-called inclinometer or tilt sensor. At present, fixing by means of angle measurement is an indirect method which is used when it is difficult to provide the object to be measured with necessary fixing points which are clearly visible and which position can not be recognized otherwise. Angle measurement fixings have been performed using fixing points on the container or on structures outside the object to be measured and using an angle value obtained from the angle measurement device, whereby the coordinate systems could be mathematically combined. The permanent marks are attached to the container or to the frame structures of a factory wall, for example, in vicinity to the basic oxygen furnace. When angle measurements were used in the known methods, the angle measurement device informs the measuring device of the position of the object or container in relationship to the known surroundings.
In both direct and indirect angle measurement fixing methods, the permanent marks can be, for example, small plates, cylinders, spheres or other regularly shaped objects made from a material which reflects laser radiation.
EP 1 234 193 B1, which has a counterpart U.S. Pat. No. 6,922,251 the entire specification of which is incorporated by reference to Kirchhoff et al. discloses a method for measuring the refractory lining of a metallurgical container by means of a laser scanner wherein the laser scanner is positioned centrally in front of the container in preparation of the measuring step to establish a precise definition of the position of the laser scanner relative to the container with the aid of permanent marks attached to the said container. Once the container has been emptied, measuring of the interior of the container can be performed in that a laser beam which can be deflected horizontally and vertically scans the inner surface of the container. The laser beams reflected from the refractory lining are received and are processed in accordance with their time of flight. Since also the position of the receiver is well known relative to the laser head and the respective angle position of the laser head has been determined for each individual laser beam, the shape of the surface of the refractory lining can be reconstructed from the data generated. Advantageously the container is not only scanned in its horizontally tilted position, but scanning is also done in two additional tilted positions, for example 20° upwards and approximately 20° downwards to make possible scanning the entire interior of the vessel.
After the central scan of the refractory lining, also a left and right scan can be performed in the method known from EP 1 234 193 B1 to also scan the entire side wall near the opening of the vessel by moving the laser scanner into left or right positions with respect to the vessel. The laser scanner has to be moved because the vessel can be tilted about its horizontal axis only but not to the left or right.